Brush-less motors are widely used in the market. The brush-less motor has a permanent magnet on the rotor side, and a position sensor senses a magnetic pole of the permanent magnet for switching a phase excitation, thereby driving the brush-less motor. A controller of the brush-less motor is formed of two major sections: one is a position sensor for sensing a rotational position of the rotor, and the other one is a driver for driving the motor. FIG. 22 shows a structure of a conventional motor controller.
In FIG. 22, driver 602 includes dc power supply 615, which powers position sensor 603 via wiring section 616. Power incoming section 617 works as a power supply for position sensor 603, which is equipped with position sensors (e.g. Hall IC) 611, 612, 613 sensing a magnet pole position of the rotor of motor 610 and outputting a phase-excitation switching signal. Driver 602 includes inverter circuit 690 which powers respective phase-coils of motor 610, and power switching circuit 680 which controls power-switching of inverter circuit 690. Wiring section 616 is formed of five electrical cables in total, i.e. two power cables and three signal cables. Wiring section 616 wires position sensor 603 to driver 602.
Inverter circuit 690, having six power transistors, is powered by dc power supply 629 and coupled to three-phase motor 610 via cables U, V, W.
Hall ICs 611, 612, 613 sense a magnetic pole position of the rotor of motor 610 and output phase-excitation switching signals CS1, CS2, CS3 respectively. Those signals are supplied to driver 602 via wiring section 616, and in general, they have a phase difference of 120 degrees in electric angles from each other and are output in the form of rectangular pulse.
Signals CS1, CS2, CS3 supplied to driver 602 are fed into power-switching circuit 680 via buffer circuits 681, 682, 683 respectively. Power-switching circuit 680 produces a signal which switches a powering and a phase-excitation of respective phase-coils of motor 610, and outputs powering signals UH, VH, WH, UL, VL, WL of the six power transistors of inverter circuit 690 in the form of rectangular pulse.
FIG. 23 shows waveforms of the brush-less motor being driven by the rectangular-pulse driving method. Power-switching circuit 680 produces a power signal for the six power transistors based on phase-excitation switching signals CS1, CS2, CS3 supplied from Hall ICs 611, 612, 613. This power signal drives inverter circuit 690 to perform switching operation. As a result, a current shaping like a rectangular wave such as Iu passes through, e.g. cable U.
In the foregoing prior art, the phase-excitation switching signals are transmitted from the motor to the driver through three cables in parallel; however, the signals can undergo a parallel-serial conversion and are transmitted through two differential output cables. This instance is disclosed in Japanese Patent Application Non-Examined Publication No. H10-206187.
The conventional controller of the brush-less motor needs two cables for transmitting dc power supply 615 to position sensor 603, and three cables (two cables in the case of the differential output cables) for transmitting phase-excitation switching signals CS1, CS2, CS3 to driver 602. As many as five cables in total (four cables in the case of the differential output cables) are thus needed, so that a fewer cables have been required for improving efficiency of assembling the controller.
FIG. 24 shows a structure of each one of Hall ICs 611, 612, 613. As shown in FIG. 24, Hall element 636, which senses a magnetic pole position, outputs a signal, and operation amplifier 637 amplifies the signal, then open collector 638 outputs the signal amplified. In the case of a signal at logic level H, the cable cannot carry a current, so that the cable falls into a high-impedance status. The cable becomes thus vulnerable to noises, particularly when the signal needs a long distance transmission.
Use of a shielded cable is one of measures for avoiding this problem; however, it is expensive and difficult to get the shielded cable containing five cables insulated from each other. Since this idea causes time-loss and cost-increase, another idea for increasing the productivity has been required.